Polycarboxylic acids have applicability in a wide range of fields, and in particular in the field of non-formaldehyde finishing agents. In fact, a number of references disclose the use of polycarboxylic acids for this purpose. C. Q. Yang discloses the use of maleic acid copolymers with citric acid as non-formaldehyde finishing agents in “Nonformaldehyde Durable Press Finishing of Cotton Fabrics by Combining Citric Acid with Polymers of Maleic Acid,” Textile Res. J. 68:457–464. PCT publication WO 96/26314 describes the use of maleic acid oligomers for treating cellulose fabrics in the presence of sodium hypophosphite as a cross-linking catalyst.
Dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid have been historically difficult to polymerize into homopolymers, unlike their mono-carboxylic acid cousins such as acrylic acid. Several publications disclose the polymerization of maleic acid via complexation with other materials such as polyvinylpyrrolidone or via the use of maleate salts with either strong bases under specialized conditions or peroxide or metal catalysts.
U.S. Pat. No. 6,277,152 and PCT publication WO 01/21677 both disclose the synthesis of polymaleic acids with phosphorous reducing agents to form phospho/maleic acid polymers for use as cotton finishing agents. Both references disclose combining maleic acid with a phosphorous reducing agent and a persulfate free radical generator to form the phospho/maleic acid polymers. However, neither of the disclosed reactions for the production of these polymers proves satisfactory. Both result in reactions that stop far short of completion and have poor color and clarity values, a less than desirable quality for finishing agents of white cotton fabrics.
Accordingly, the need remains for an improved process for the production of polycarboxylic acids using phosphorous-containing reducing agents.